Operators are using unlicensed frequency bands to augment their services supplies, which is being studied in 3GPP and called Licensed-Assisted-Access (LAA). When LTE works in unlicensed frequency bands, the key issue is to ensure fair coexistence with Wi-Fi system and other systems.
Currently, Wi-Fi system designs Enhanced Distributed Channel Access (EDCA) to support prioritized quality of service (QoS), wherein four access categories (ACs) are defined. Each AC is characterized by specific values for a set of access parameters (e.g., defer period, contention window size, transmit opportunity) that statistically prioritize channel access for one AC over another.
Naturally, LAA systems coexisted with Wi-Fi system should also support QoS with multiple Listen-Before-Talk (LBT) priority classes. Downlink LBT procedure for LTE-LAA has been discussed in 3GPP and it recommends a LBT mechanism operating similar to channel access in Wi-Fi for LAA downlink transmission.
Until now, LAA lacks solutions in which multiple QoS requirements are processed using LBT operation. Therefore, it becomes particularly important to design a mapping relationship between multiple QoS priority classes and multiple Listen-Before-Talk (LBT) priority classes and potential signaling to support different QoS in LTE-LAA.